The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

Najas marina
Najas marina
(spiny waternymph)
Native Transplant
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Najas marina L.

Common name: spiny waternymph

Synonyms and Other Names: Najas gracilis (Morong) Small, Najas major All., Najas marina var. recurvata DudleyNajas major var. angustifolia A. Braun ex K. Schum, spiny water nypmh, spiny-leaf naiad alkaline water-nymph, holly-leaf naiad, holly-leaved water nymph, large naias, saw tooth, marine naiad, marine water nymph, 



Taxonomy: available through www.itis.govITIS logo

Identification: Najas marina is a submersed plant with brittle stems that are often branched toward the upward portion of the plant. Stems branch distally, 6-45 cm ´ 0.5-4 mm.  The internodes (0.3-11cm) of the stem usually have conspicuous, brownish, prickly teeth. The leaves are opposite or sometimes in whorls of three, 0.5 to 4.0 cm long and 0.4-4.5mm wide, and have 8-13 triangular (multicellular) teeth along the leaf margins and prickles along the midrib on the underside of the leaf.  Leaf apex acute, with 1 tooth,.  Leaves spreading to ascending with age and stiff in age.  Sheaths 2--4.4 mm wide.

Plants are dioecious with the male and female flowers borne on separate individuals. The flowers are solitary in the leaf axils. The female flowers produce ovoid seeds 2.0 to 4.5 mm long that have 3 to 4-angled areolae that are irregularly arranged (http://el.erdc.usace.army.mil/pmis/plants/html/najas_ma.html).

Flowers 1 per axil, staminate and pistillate on different plants. Staminate flowers in distal to proximal axils, 1.7-3 mm; involucral beaks 2-lobed, 0.3-0.7 mm; anthers 4-loculed, 1.7-3 mm. Pistillate flowers in distal to proximal axils, 2.5-5.7 mm; styles 1.2-1.7 mm; stigmas 3-lobed. Seeds not recurved, reddish brown, ovoid, 2.2-4.5 ´ 1.2-2.2 mm, apex with style situated at center; testa dull, 10-15 cell layers thick, pitted; areoles irregularly arranged, not in distinctive rows, not ladderlike, 3-4-angled, longer than broad, end walls slightly raised. 2n = 12 (Europe).

With its prickly internodes and prickles along the abaxial surface of the leaves, Najas marina is the easiest of our Najas to recognize.

Size: Perennial growing to 0.5m.

Native Range: Najas marina is native to Caribbean Territories, California, Hawaii, continental US, and Eurasia

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Nonindigenous Occurrences:

Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Najas marina are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
IL199320082Upper Illinois; Upper Mississippi Region
IN199020082Kankakee; St. Joseph
MI193820086Au Gres-Rifle; Great Lakes Region; Muskegon; Northeastern Lake Michigan; Pine; Western Lake Erie
MT201820201Middle Clark Fork
NE200820081Missouri Region
NY186420085Great Lakes Region; Indian; Lake Ontario; Oswego; Seneca
OH195920184Lake Erie; Middle Ohio-Laughery; Sandusky; Western Lake Erie
OK200820081Arkansas-White-Red Region
PA200820081Upper Juniata
WI196820179Fox; Manitowoc-Sheboygan; Middle Rock; Milwaukee; Pike-Root; Upper Fox; Upper Fox; Upper Rock; Wolf

Table last updated 9/8/2020

† Populations may not be currently present.

Ecology: Spiny naiad is found in 3' or more deep water in brackish or highly alkaline ponds, lakes, and coastal and inland marshes at elevations up to 1000 m in United States (Calflora Plant Observation Library).

Plants are reported to reproduce by seed and fragmentation (Tarver et al. 1986). Studies by Vierssen (1982) have shown seed germination of N. marina to be best in decomposing organic matter, at 24° C under dark conditions. It is in flower from September to November, and the seeds ripen from September to November. The plant prefers light (sandy), medium (loamy) and heavy (clay) soils. The plant prefers acid, neutral and basic (alkaline) soils and can grow in saline soil. It can grow in semi-shade (light woodland) or no shade.

Means of Introduction: Introduced via solid ballast.

Agami and Waisel (1986) found the germination of N. marina to be increased after passing through the digestive tract of mallard ducks, and postulate that ducks may be a major factor in long range dispersal of N. marina.

Status: Found in Lake Ontario; widespread throughout the Great Lakes region (U.S.EPA 2008).

Impact of Introduction: Najas marina can sometimes interfere with boating and fishing. It poses a realistic nuisance threat to ecosystems (U.S.EPA 2008). However, the plant is considered to be an excellent waterfowl food (Tarver et al. 1986).

Remarks: This species is potentially a range expander rather than truly nonindigenous to the Great Lakes region, based on a review of current literature.

This species is currently considered non-native in GLANSIS, based on Mills et al. (1993) paper, which states, “Spiny naiad, a plant preferring to grow in brackish and alkaline waters, was first found in North America in 1864 in central New York's Onondaga Lake near Salina, New York (Stuckey 1985). The plants were growing near a salt mine in brackish water. Soon after this initial record, the plant was discovered in other areas of central New York. Spiny naiad is also known from the western Great Lakes region where it invaded in the 1930s. Fossil records of this plant from the midwest indicate that it was present in North America prior to glaciation, supporting debate about whether the newly discovered populations were indigenous or non-native. Two interpretations of the plant's distribution in the Great Lakes have been outlined by Stuckey (1985). He theorizes that the plant was pushed south during glaciation and reinvaded glacial lakes when the ice receded. He suggests that the species persisted in areas where the habitat remained favorable and reinvaded some areas, such as the western Great Lakes region, more recently. The introduction of the plant from Europe or another region where it is common in habitats made brackish and alkaline by human activities (such as areas around salt mines) is also possible. Central New York was a very active botanical center in 1864 and the possibility that the plant was overlooked for years is unlikely. The area around Onondaga Lake has been industrialized since the early 1800s when humans began developing the salt resources around the lake. The salt from this area was transported into other parts of the United States and the salt industry had the power to instigate the construction of the Erie Canal (Murphy 1978). We consider the introduction of spiny naiad into the industrialized area around Onondaga Lake to be a more likely scenario than the persistence of preglacial populations. Spiny naiad is now also known from Europe, Asia, Africa, Australia, South America, and Central America (Stuckey 1985).”

The classification of this species is a source of ongoing contention in Great Lakes states, and some environmental managers consider it to be naturalized in the region, though they note that its range appears to slowly be expanding (Nault, M., 2017, pers. comm). Its cosmopolitan nature and sporadic distribution around the world is likely due to its very specific environmental needs, which include brackish, highly alkaline waters. No active management is currently being conducted on N. marina in Wisconsin, and further research is needed to determine its ultimate status in the Great Lakes.

References: (click for full references)

Agami, M. and Y. Waisel. 1986. The role of mallard ducks (Anas platyrhynchos) in distribution and germination of seeds of the submersed hydrophyte Najas marina. Oecologia (Berlin) 68: 473-475.

Agami, M. and Y. Waisel. 1988. The role of fish in distribution and germination of seeds of the submerged macrophytes Najas marina L. and Ruppia maritima L. Oecologia 76(1): 83—88.

Flora of North America.  2008. www.eFloras.org

Haynes, R. R. 1979. Revision of North and Central American Najas (Najadaceae). Sida 8: 34-56.

Lembi, C. A. 2003. Aquatic Plant Management. Purdue University Cooperative Extension Service. 20 pp.

Minnesota Department of Natural Resources (MN DNR). 2013. Najas marina  L.: Sea Naiad. Available http://www.dnr.state.mn.us/rsg/ Accessed 23 April 2013.

Stuckey, R. L. 1985. Distributional history of Najas marina (spiny naiad) in North America. Bartonia 51: 2--16.

Tarver, D. P., J. A. Rogers, M. J. Mahler, and R. L. Lazor. 1986. Aquatic and Wetland Plants of Florida. Third Edition. Florida Department of Natural Resources, Tallahassee, Florida.

Triest, L., J. van Geyt, and V. Ranson. 1986. Isozyme polymorphism in several populations of Najas marina L. Aquatic Bot. 24: 373--384.

U.S. EPA (Environmental Protection Agency). (2008) Predicting future introductions of nonindigenous species to the Great Lakes. National Center for Environmental Assessment, Washington, DC; EPA/600/R-08/066F. Available from the National Technical Information Service, Springfield, VA, and http://www.epa.gov/ncea.

Vierssen, V. W. 1982. Some notes on the germination of seeds of Najas marina. Aquatic Botany 12: 201-203.

Viinikka, Y. 1973. The occurrence of B chromosomes and their effect on meiosis in Najas marina. Hereditas (Lund) 75: 207--212.

Wentz, W. A. and R. L. Stuckey. 1971. The changing distribution of the genus Najas (Najadaceae) in Ohio. The Ohio Journal of Science 7(15): 292—302.

Other Resources:

Author: Cao, L, and L. Berent

Revision Date: 12/4/2019

Citation Information:
Cao, L, and L. Berent, 2020, Najas marina L.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=2674, Revision Date: 12/4/2019, Access Date: 10/21/2020

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.


The data represented on this site vary in accuracy, scale, completeness, extent of coverage and origin. It is the user's responsibility to use these data consistent with their intended purpose and within stated limitations. We highly recommend reviewing metadata files prior to interpreting these data.

Citation information: U.S. Geological Survey. [2020]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [10/21/2020].

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